Single-phase quasi-Z Source Inverter Research Articles

A simplified space vector modulation for the single-phase active power decoupling quasi-Z-source inverter

The double-line frequency ripple power of the single-phase quasi-Z source inverter (qZSI) will result in a large designed qZS impedance on the dc side, which can be greatly reduced by the coupled-type active power decoupling (APD) method. However, the traditional sinusoidal pulse width modulation (SPWM) for the APD-qZSI needs extravagant APD storage capacitance and may cause abnormal operation under low load conditions. Classical space vector modulation (SVM) has higher flexibility and dc-link voltage utilization, but it cannot be directly applied to the APD-qZSI. In this paper, a simplified SVM method for the coupled-type APD-qZSI is proposed, where the switching time sequence is transformed to carrier-based pulse width modulation, so the shoot-through control of the qZSI is easy to implement. Next, the passive component parameters and normal operation range of the traditional SPWM and the proposed SVM are analyzed and compared. The proposed SVM has a smaller APD storage capacitance but a slightly larger ac side filter inductance. In addition, the decreased current of the APD branch under SVM can help suppress the abnormal operation of the inverter, so the APD-qZSI can operate at a lower load condition. Finally, experimental results validate the effectiveness and superiority of the proposed SVM method.

Comparison of FCS-MPC Strategies in a Grid-Connected Single-Phase Quasi-Z Source Inverter

This paper compares two finite-control-set model predictive control (FCS-MPC) strategies in the context of a grid-connected single-phase quasi-Z source inverter (SP-qZSI). Both schemes use discrete-time models of the inductor current and capacitor voltage for the DC side, as well as the output current on the AC side. To enhance the converter’s performance, given the non-minimum phase characteristics of the DC side, a long prediction horizon is implemented for the predictive control. However, a horizon of this nature can be highly demanding in terms of processing load, rendering it inapplicable for some microcontrollers. To address this issue and mitigate the processing load, an alternative control strategy is presented that divides the total number of candidate solutions to be evaluated into smaller segments. The performance of the two control strategies is compared using total harmonic distortion (THD) and simulation times as evaluation metrics. The results indicate that the proposed strategy achieves significantly shorter simulation times than the compared control strategy when increasing the prediction horizon. Additionally, a reduction in the THD was observed in the proposed strategy, reaching an average of 2.8%, which is lower than the compared strategy that exhibited THD close to 3.5%.

Ripple Vector Cancellation Modulation Strategy for Single-Phase Quasi-Z-Source Inverter

The double-frequency (2ω) power flows through the DC side of the single-phase quasi-Z-source inverter (QZSI) leads to the 2ω voltage ripple of capacitors and 2ω current ripple of inductors. This paper proposes a ripple vector cancellation modulation strategy (RVCMS) based on the thought of ripple vector cancellation. By analyzing the mechanism of ripple generation and transmission, we can obtain a variation of a shoot-through duty cycle to generate a compensated 2ω ripple used to cancel the 2ω current ripple of inductors caused by the 2ω ripple of DC link current, and the 2ω compensated variation of a shoot-through duty cycle with a specific amplitude and phase is added to the constant shoot-through duty cycle. Finally, simulation and experimental results demonstrate the correctness and effectiveness of the proposed modulation strategy for the single-phase QZSI.

Common Mode Voltage Reduction in a Single-Phase Quasi Z-Source Inverter for Transformerless Grid-Connected Solar PV Applications

The quasi-Z-source inverter (qZSI) is becoming a popular inverter topology that can buck or boost input voltage without a dc–dc converter and hence can be used in transformerless configuration. Due to its single-stage conversion, the qZSI can be used as an efficient transformerless grid-tie inverter. However, the common mode current is a major problem in transformerless topologies due to the absence of galvanic isolation. This paper proposes a modified pulsewidth modulation (PWM) technique to control the qZSI, along with two extra semiconductor switches, to reduce the common mode current. The proposed method offers an efficient solution for grid integration of solar photovoltaic systems. The proposed topology has the following features: 1) uses phase-leg shoot-through for boosting the dc voltage to the required level which eliminates the additional dc–dc converter; 2) eliminates the PWM deadtime and provides freewheeling through additionally connected switches; 3) minimizes the common mode current by modifying the PWM and adding additional switches at the output side of inverter; and 4) avoids the conduction of body diode of H-bridge which has poor reverse recovery characteristics. The proposed topology can efficiently control the reactive power, and the suitable PWM scheme is also reported. Simulation results have been performed with the Standard Test conditions of the photovoltaic panel. Experimental results for a single-phase 500-W prototype are presented to validate the proposed PWM scheme for the qZSI topology.

A ripple suppression strategy based on virtual self-injection APF for quasi-Z source inverter

The power flows between the DC side and AC side of single-phase quasi-Z source inverter (QZSI) causes double-frequency (2ω) voltage ripple of capacitors, current ripple of inductors. This paper proposes a virtual self-injection active power filter (APF) ripple suppression strategy for the single-phase QZSI without changing the circuit structure, and the 2ω ripple is suppressed by controlling the shoot-through duty cycle based on the thought of ripple vector cancellation. The 2ω ripple model and its generation mechanic for single-phase QZSI are presented through the analysis of the power flows and small signal model for quasi-Z network. Simulation results verify the proposed ripple suppression strategy can effectively reduce the 2ω current ripple of inductors from 18.38% to 3.54%.

Current Ripple Damping Control to Minimize Impedance Network for Single-Phase Quasi-Z Source Inverter System

The single-phase quasi-Z source inverter (qZSI) topology has recently attracted attention for single-phase grid-tie photovoltaic (PV) applications. However, due to the inherent second-harmonic power flow in single-phase systems, a large qZS network is required to reduce the second-harmonic component of currents and voltages on the dc side. Minimization of the qZS network remains an open issue. This paper proposes a technique that minimizes the qZS capacitance and inductance of the single-phase qZSI topology by employing dc-side low-frequency current ripple damping control. Through analysis of power flow, a second-harmonic power model is derived and the ripple power is analyzed for minimization of the qZS network. A current ripple damping control is proposed to ensure suppression of second-harmonic power flow through the inductors. Simulation and experimental results verify the theoretical analysis, damping control, and the proposed design minimization of the qZS network for the single-phase topology.